<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      padding: 0;
      margin: 0;
      box-sizing: border-box;
    }

    .box {
      display: grid;

      /* grid-template-columns: 100px 100px 100px; */
      grid-template-columns: 1fr 1fr 1fr;
      column-gap: 24px;
      row-gap: 12px;
      width: 300px;
      height: 300px;
      border: 1px solid red;

    }

    .item {
      background-color: pink;
      color: #fff;
    }

    .container {
      display: grid;
      grid-template-areas:
        'header header header'
        'sider content content'
        'footer footer footer';
    }

    .header {
      grid-area: header;
    }

    .footer {
      grid-area: footer;
    }
  </style>
</head>

<body>

  <div class="box">
    <div class="item">
      nihao
    </div>
    <div class="item">
      nihao
    </div>
    <div class="item">
      nihao
    </div>
    <div class="item">
      nihao
    </div>
    <div class="item">
      nihao
    </div>
    <div class="item">
      nihao
    </div>
    <div class="container">
      <header class="header">
        ewe
      </header>
      <div class="sider"></div>
      <div class="content"></div>
      <footer>

      </footer>
    </div>

  </div>
</body>

</html>